[llvm] [IR] Add nowrap flags for trunc instruction (PR #85592)

[Yingwei Zheng via llvm-commits]

================
@@ -368,11 +368,19 @@ bool Instruction::isOnlyUserOfAnyOperand() {
 }
 
 void Instruction::setHasNoUnsignedWrap(bool b) {
-  cast<OverflowingBinaryOperator>(this)->setHasNoUnsignedWrap(b);
+  if (auto *Inst = dyn_cast<OverflowingBinaryOperator>(this)) {
+    Inst->setHasNoUnsignedWrap(b);
+  } else {
+    cast<TruncInst>(this)->setHasNoUnsignedWrap(b);
+  }
 }
 
 void Instruction::setHasNoSignedWrap(bool b) {
-  cast<OverflowingBinaryOperator>(this)->setHasNoSignedWrap(b);
+  if (auto *Inst = dyn_cast<OverflowingBinaryOperator>(this)) {
+    Inst->setHasNoSignedWrap(b);
+  } else {
+    cast<TruncInst>(this)->setHasNoSignedWrap(b);
+  }
----------------
dtcxzyw wrote:

```suggestion
  if (auto *Inst = dyn_cast<OverflowingBinaryOperator>(this))
    Inst->setHasNoSignedWrap(b);
  else
    cast<TruncInst>(this)->setHasNoSignedWrap(b);
```

https://github.com/llvm/llvm-project/pull/85592